<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="js/vue.js"></script>
</head>

<body>
    <div id="app">
        <input type="text" v-model="n1">
        <select v-model="opt">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>

        <input type="text" v-model="n2">

        <input type="button" value="=" @click="calc">

        <input type="text" v-model="result">
    </div>


    <script>
        var vm = new Vue({
            el: '#app',
            data: {
                n1: 0,
                n2: 0,
                result: 0,
                opt: '+'
            },
            methods: {
                calc() {
                    /* switch(this.opt){
                        case '+':
                        this.result = parseInt(this.n1)+parseInt(this.n2)
                        break;
                        case '-':
                        this.result = parseInt(this.n1)-parseInt(this.n2)
                        break;
                        case '*':
                        this.result = parseInt(this.n1)*parseInt(this.n2)
                        break;
                        case '/':
                        this.result = parseInt(this.n1)/parseInt(this.n2)
                    } */

                    var codeStr = 'parseInt(this.n1)' + this.opt + 'parseInt(this.n2)'
                    this.result = eval(codeStr)
                }
            },
        })
    </script>
</body>

</html>